This invention relates to a lubricating oil supplying system for a two cycle engine and more particularly to an improved apparatus and method for controlling the supply of lubricant to a two cycle engine.
The advantages of two cycle internal combustion engines in so far as simplicity and high output for a given displacement are well known. Conventionally it has been the practice to lubricant two cycle engines by mixing lubricant with the fuel consumed by the engine. However, this method of lubrication, although simple and low in cost, does not provide adequate control for the amount of lubricant consumed. That is, when fuel and lubricant are mixed, it is necessary to insure that the mixture will satisfy the most severe operating condition. As a result, excess lubricant is supplied under most operating conditions.
To avoid these problems and to insure better lubrication, lubricant control and reduction of lubricant consumption, it has been proposed to employ a separate lubricating system for two cycle engines. Such separate lubricating systems employ a pump that pumps lubricant to the engine for its lubrication. This lubricant may be delivered to the induction system for the engine, directly to components to be lubricated or a combination of the above.
Normally a form of reciprocating type of pump is employed which is driven by the engine for supplying the lubricant. Such pumps have the advantage of providing accurate control of the amount of lubricant delivered and are capable of delivering relatively small amounts of lubricant. However, the amount of lubricant delivered by such a pump is related directly to engine speed and the lubricant requirements of the engine are not necessarily so related.
One way in which the amount of lubricant pumped has been controlled is by controlling the effective stroke of the lubricant pump either by changing the stroke or by use of a spill type valve which in effect changes the stroke pump. FIG. 1 is a graphical view showing the way in which lubricant is controlled with conventional systems and the actual lubricant requirements for the engine. This figure is a graphical view showing the relationship of engine speed to lubricant amount. Normally, the amount of lubricant supplied to the engine is controlled along a curve as shown by the curve "a" wherein the output of the lubricating pump is varied dependent upon accelerator or throttle valve position. It will be seen that the amount of lubricant supplied is increased along a slope from a given engine speed up until a maximum amount and then is held constant.
The dotted line curve "b" shows the actual lubricant requirements for the engine. As may be seen, the approximation curve using throttle valve or accelerator position can relatively closely match engine lubricating requirements under a wide range of steady state conditions.
However, because the lubricant control is varied in response to throttle valve position and throttle valve position changes more rapidly than engine speed, this type of control can produce excess lubricant under transient conditions. This is depicted by the dot/dash line curve "c" in FIG. 1 which shows the effect of the operator suddenly opening the throttle valve. When this occurs, the lubricant amount is rapidly increased even though the engine speed has not increased in the same proportion.
In addition to the aforenoted defects, the use of mechanisms to change the stroke of the pump or spill valves require relatively expensive pumps and can be subject to mechanical failure.
It is, therefore, a principal object of this invention to provide an improved lubricating oil supply system for a two cycle engine.
It is a further object of this invention to provide a lubricating oil supply system for a two cycle engine wherein the amount of lubricant supplied to the engine can be closely tailored to the actual running condition, even under transient conditions.